Interestingly enough, I found apologizing to myself actually fed into my feelings of guilt and blame. I've had the most peace when I focus on loving myself - I think the forgiveness part is natural when you love yourself as much as you deserve.
I also remind myself regularly that without living through my experiences, I might never have gotten to where I am now, and I am so grateful for where I am now. So I am grateful for my experiences, even the bad ones.
Louise Hay has this affirmation I really like for this - "I bless the past with love and let it go."